The present invention relates to exhaust gas filters, and more specifically, to an exhaust gas filter for use in a diesel engine, wherein carbon soot exhausted from the diesel engine is collected using a ceramic filter and is burned in said ceramic filter so that the volume of carbon soot discharged from the engine can be reduced.
In order to collect carbon soot exhausted from a diesel engine, the following exhaust gas filters for a diesel engine have conventionally been designed: a filter made from metal wire mesh coated with alumina, a foamed ceramic filter having a porous structure made by adding a foaming agent to the ceramic, a ceramic fiber mat, and a honeycomb shaped ceramic monolith filter. Of these filters, the honeycomb shaped ceramic monolith filter is approximately 90% efficient for soot collection and has a low pressure drop, therefore it is expected to be effective for removing carbon soot in exhaust gas. In general, a ceramic monoloth filter for diesel engine exhaust gas is of a honeycomb structure comprising a plurality of cells mainly composed of CORDIERITE and produced by an extrusion process. Every other opening at both opposite ends of the honeycomb cell structure, located at the upstream and downstream sides with respect to the direction of flow of the exhaust gas, is clogged with a material like cement, which has a very low porosity and is approximately 10 mm in length. That is, a cell channel clogged at the upstream side is opened at the downstream side and an adjacent cell channel is conversely clogged, so that each cell channel functions as either an entrance or exit channel for exhaust gas. As a result, substantially all of the carbon soot in the exhaust gas is collected on the cell walls. On the other hand, a pressure drop of exhaust gas at the filter increases with an increase in the carbon soot deposition on the filter and the engine performance is deteriorated. Accordingly, in order to maintain good engine performance, the filter regenerates itself by afterburning the deposited carbon soot after the quantity of deposited carbon soot reaches a predetermined value. There has been a long felt need for an exhaust gas filter for a diesel engine having a honeycomb structure, wherein deposited carbon soot is ignited and burns by propagation over the surfaces of the cell walls, to burn the soot up completely, and then, the filter is easily and repeatedly renewed.